1. Field of the Invention
The present invention relates to video display monitors having a low power or sleep mode of operation.
2. State of the Art
Recent studies have concluded that during normal business hours a large percentage of electric power is consumed by computing equipment. The same computing equipment, however, is typically not used on a continuous basis, but rather is used at intervals. Despite this usage at intervals, computing equipment is typically left on continuously during business hours and often around the clock. Such practice wastes energy, since the computing equipment, even though it is not being used, continues to draw a significant amount of power. In view of this situation, the Energy Star regulation has been advanced, which sets forth guidelines for the intelligent conservation of energy by computing equipment.
In a typical small computer, a large share of energy is consumed by the video display monitor. In a typical small system, the CPU may consume about 50 to 80 W, and the display may consume about 80 W (15" display) to 135 W (17" display). Video display monitors therefore offer considerable potential for energy savings. According to the Energy Star regulation, when horizontal and vertical sync signals are not being applied to the video display monitor by the host CPU, the video display monitor should switch off. The power consumption in this mode (standby mode) should be below 15 W, preferably below 5 W.
The most common approach to fulfill the Energy Star regulation is to keep the main power supply running but to switch off all unnecessary supply lines. Usually only a few low-power supply lines will be kept alive during standby mode operation. Because the main power supply is running at very low output power, the efficiency of the supply will drop considerably. Although only 1 or 2 W power is needed, the main power supply may consume between 5 to 10 W.
Another method is to use an auxiliary power supply to control the main power supply. Usually, a simple switching-type regulator is used for this purpose. The cost for such an auxiliary supply may vary depending on the output power and input voltage range, but is not insignificant. Using this arrangement, power consumption during standby operation is in the range of 2 to 4 W.